Feeling the Heat

Drought conditions have changed much since last summer. More of the country is experiencing lower levels of drought, but less of the country is being hit with the extreme and exceptional drought that caused so much trouble last year.

As of May 29, only 36 percent of the contiguous U.S. was experiencing no drought or abnormal dryness — much lower than last year’s 69 percent. But on the bright side, the percentage of the U.S. suffering from extreme or exceptional drought has decreased from 13 percent to 5 percent, according to the U.S. Drought Monitor. The monitor is a drought tracking and measurement tool that is a collaboration of several organizations, including the National Drought Mitigation Center, the USDA and the National Oceanic and Atmospheric Administration. It uses a ranking system that begins at D0 (abnormal dryness) and moves through D1 (moderate drought), D2 (severe drought), D3 (extreme drought) and D4 (exceptional drought). Exceptional drought’s impacts include widespread crop and pasture losses, as well as shortages of water in reservoirs, streams and wells, creating water emergencies.

Nearly 12 percent of the contiguous United States fell into the “exceptional” classification during July 2011, peaking at 11.96 percent on July 12 — the highest level in the monitor’s 12-year history. Currently, less than one percent of the contiguous U.S. is experiencing the most serious level of drought.

Today, 64 percent of the contiguous U.S. is experiencing at least abnormal dryness, compared to 31 percent last year. However, of that 64 percent, only five percent is classified as extreme to exceptional drought. If you were getting hit with drought last summer, there was a pretty good chance it was serious.

Effects of early spring
That’s not to say that this year is all waterfalls and daisies. “We have finished up a very difficult May for many parts of the country agriculturally, especially across the central and southern plains stretching on through the middle and lower Mississippi valley and even on up into the Eastern corn belt and the lower Midwest,” said Brad Rippey, a meteorologist with the USDA who works on the drought monitor. “A lot of these areas have come up way short on moisture in May, which is a key time for agricultural interests.”

Abnormally high temperatures in March and April provided a jumpstart to the 2012 growing season. For the lower 48 states, it was the warmest March on record. Temperatures stayed high through April and May, and the early start to growing season led to accelerated plant development. Because many plants were further along their development schedule, they required more water than in a typical spring.

“If you look at the season to date — March, April, and May — crop water demands have been considerably higher this year than normal,” Rippey said. “The reasons are the extended growing season and the above-normal temperature, which leads to higher evaporation. So you are losing moisture through heat as well as crop use.”

The higher water demands coupled with the higher temperatures have created dry soil. Even some areas of the country that have had normal amounts of rainfall are experiencing shortages of moisture in their soil because of those two factors.

Keep a weather eye on the horizon
Growers that blow off the lower levels of the drought ranking system do so at their own peril. Even D0, though it is a non-drought category, can be a harbinger of drought on the horizon.

“It serves as a warning that it is getting dry, and things could go downhill in a hurry especially if we get some heat,” Rippey said. “The hotspot right now stretches from eastern Oklahoma through the lower Ohio valley. That area started to see some dryness develop in late April and early May, now they are in a full-fledged drought because they haven’t gotten much relief.”

If you’re watching the monitor and looking for signs of an impending drought, Rippey offers this advice: if you start seeing yellow, it’s not drought yet, but you could be headed for one unless rain falls soon.

Another factor to pay attention to on the drought monitor is short-term and long-term impacts. Most short-term impacts will be in the root zone, or the topsoil moisture zone. This is primarily an agricultural impact. You see pastures and grasses browning out, you see some stress on crops like corn, soybeans or wheat. But as time marches on, the impacts start to become hydrological. At that point, you start seeing stream flow decreasing and ponds drying up. If a drought lingers for longer than six months, recovery is very slow. All the rain that falls has to go toward replenishing soil moisture.

Texas was one of the states hit hardest by last year’s drought. But steady rainfall over a seven-month period from October to April has helped Eastern and Northeastern Texas recover from the drought. Other parts of the state aren’t faring as well. According to the Lower Colorado River Authority, Lakes Buchanan and Travis, the Central Texas region’s water supply reservoirs, are currently half full. The lakes were 70 percent full in May 2011, but fell to 37 percent full by Dec. 1.

Looking forward
There may be a light at the end of the tunnel. For the last two years, the U.S. has been influenced by a La Niña climate pattern — cool water in the tropical Pacific Ocean. When a La Niña takes place, it usually correlates to hot and dry conditions across the Southern U.S.

However, there seems to be indications that those tropical waters could warm in the coming months, causing an El Niño to develop. As a weather phenomenon, El Niño typically leads to heavy precipitation across the southern tier of the country during fall, winter and spring. That would cut through the heart of the drought areas in the Southwest, West Texas and the Southeast.

“(These indications) are by no means a guarantee,” Rippey said. “But if that were to happen it would certainly be a boon for folks in the southern U.S. that have been dealing with drought for a long time. It’s something to keep in mind — perhaps relief is on the way.”
 

For more: U.S. Drought Monitor, http://droughtmonitor.unl.edu/